This invention relates to pressure relief valves. More specifically, this invention relates to a relief valve for limiting the discharge pressure from a compressor providing air to an aircraft engine and cabin pressurization system.
Relief valves are commonly used in aircraft for preventing excessive pressure levels of air supplied to the engine. Typically, the relief valve responds to the discharge pressure of a compressor to limit the discharge pressure level to a predetermined maximum, and thereby protect the engine against possible damage due to excessive pressure levels.
A wide variety of relief valves are available throughout the prior art. However, in aircraft applications, one major design criteria is that the relief valve must be relatively insensitive to variations in altitude. That is, it is desirable to limit the maximum allowable discharge pressure of the compressor to an absolute value independent of aircraft altitude.
Many prior art systems have been developed in an attempt to regulate closely the discharge pressure of a compressor in an aircraft environment. Some of these systems include relatively complex pressure differential venturi arrangements for controlling the driving speed of the compressor, such as that shown in U.S. Pat. No. 3,207,422. Others include pressure differential systems in combination with relatively expensive bellows devices, such as that shown in U.S. Pat. No. 2,316,416. Still other systems attempt to overcome altitude sensitivity by providing a metallic bellows or the like which has been evacuated to a nearly zero pressure or other suitable reference pressure. However, these systems are not entirely satisfactory in that they comprise relatively complex and expensive relief valve arrangements. Moreover, when a bellows is used, the bellows is susceptible to leakage due to long term aging, vibration failure, and puncture.
This invention overcomes the problems and disadvantages of the prior art by providing an improved relief valve particularly for use with aircraft engine and cabin pressurization systems. The invention includes a diaphragm-operated valve member responsive directly to the pressure differential across a venturi for controllably relieving a portion of the compressor discharge flow to atmosphere.